Field of the Invention
The present invention relates to stitch skipping detection of a sewing machine which optically detects whether an upper thread, which is picked up from an upper thread loop formed by a sewing needle by a shuttle point of a shuttle, passes through the shuttle, and thereby stitch skipping by which no stitch is formed is detected.
Related Art
Needlework of a sewing machine is done as an upper thread and a lower thread form stitches as required. To be more specific, a sewing needle, through whose eye the upper thread passes, passes through fabric to protrude below the fabric, and then moves upward. When the sewing needle reaching a bottom dead point moves upward, the upper thread below the fabric is loosened, and a loop is formed. Simultaneously, a shuttle rotated in tandem with upward/downward movement of the sewing needle picks up the looped upper thread with a shuttle point at a position at which the sewing needle slightly rises from the bottom dead point. As a thread take-up lever rises at a position at which the shuttle is rotated and the shuttle point passes a given position, the shuttle is made to pass through the loop of the upper thread, and the lower thread coming out of a bobbin case to reach the fabric is entangled with the upper thread, and to form one stitch.
The conventional sewing machine detects whether the loop cuts across the bobbin case when the shuttle is made to pass through the loop of the upper thread caught by the shuttle, projects light to a front side of the bobbin case from a direction inclined with respect to a rotation center line of the shuttle, optically detects a change in light intensity of reflected light by means of a photoelectric detector, and detects generation of stitch skipping by which a knot of the upper thread and the lower thread is not formed (for example, see JP-A-2000-197786).
However, in the conventional sewing machine, the light is projected in the front of the bobbin case. However, since the bobbin case is made of a metal and generally has luster, a state of the reflected light is greatly changed by slight vibration or rattle during needlework. The influence of disturbance is increased, and it is difficult to detect passage of the thread with high accuracy.
An object of the present invention is to detect stitch skipping with higher accuracy.